St. Jude Medical Inc (STJ.N) warned Wall Street that U.S. health regulators might issue a warning letter about one of its manufacturing facilities in California as it reported another weak quarterly performance. St. Jude shares fell 5.7 percent to $40.48 in early trading on the New York Stock Exchange. During a conference call with analysts, Chief Executive Officer Dan Starks said there was a possibility that St. Jude will receive a warning letter, known in the industry as Form 483, from the U.S. Food and Drug Administration about its manufacturing facility in Sylmar, California, where it makes cardiac rhythm management products. "It's a risk, and don't be shocked if that risk is realized," Starks said. Earlier, the company posted lower quarterly net earnings on softer sales as well as restructuring and other charges. Third-quarter net earnings fell to $176 million, or 56 cents per share, from $227 million, or 69 cents per share, a year earlier. Excluding the charges, earnings were 83 cents per share, 2 cents higher than the consensus estimate on Wall Street, according to Thomson Reuters I/B/E/S. Sales fell to $1.33 billion from $1.38 billion.